Use of aqueous solutions or dispersions of copolymers of carboxyl-group-containing monomers, ethylenically unsaturated acetals, ketals or orthocarboxylic acid esters and optionally other copolymerizable monomers as leather tanning agents

ABSTRACT

The use of aqueous solutions or dispersions of copolymers composed of 
     A) from 5 to 95 mol % of ethylenically unsaturated mono- or dicarboxylic acids having 3 to 10 carbons, their anhydrides, their alkali metal, alkaline earth metal or ammonium salts, or mixtures thereof, 
     B) from 5 to 95 mol % of ethylenically unsaturated acetals, ketals or orthocarboxylic esters of the formula I ##STR1## where R 1  to R 12  independently are hydrogen or an organic radical and 
     a to d independently are 0 or 1, and 
     C) from 0 to 70 mol % of other copolymerizable monomers 
     or their hydrolysis products or polymer-analogous reaction products, as tanning agents for the self-tanning, pretanning or assist tanning of leather pelts and skin pelts or for the retanning of leather and skins.

The present invention relates to the use of aqueous solutions ordispersions of copolymers composed of carboxyl-containing monomers,ethylenically unsaturated cyclic or hemicyclic acetals, ketals ororthocarboxylic esters, with or without further copolymerizablemonomers, as tanning agents for leather. Since some of these copolymersare novel substances, the invention relates to them as well.

In the production of leather, the main tanning is usually carried outusing mineral tanning agents, such as basic chromium, aluminum and/orzirconium salts, alone or in combination with synthetic tanning agents.Subsequent retanning using natural or synthetic tanning agents serves toimprove properties of the leather such as handle, softness, graincharacteristics and body.

Examples of tanning agents in retanning are syntans, ie. water-solublecondensates of, for example, naphthalenesulfonic acid and formaldehydeor of phenolsulfonic acid, formaldehyde and urea, furthermorelignosulfonic acids, and also polymers and copolymers based on acrylicacid and other unsaturated polymerizable carboxylic acids, generally incombination with the abovementioned syntans.

For example, U.S. Pat. No. 2,205,882 (1) and U.S. Pat. No. 2,205,883 (2)describe the use of polyacrylic acid, of acrylic acid-methacrylic acidcopolymers, of styrene-maleic anhydride copolymers, of polymethacrylicacid, and of copolymers of methacrylic acid with styrene and/or methylmethacrylate for the tanning of leather. A disadvantage of theseproducts is that in many cases the desired softness and body cannot beachieved. Furthermore, these products generally have a strong lighteningeffect on the coloring. It should also be noted that products of thiskind can be employed only in a limited concentration when retanningleather, since at higher levels hardening of the leather may occur andmay lead to cracking of the grain.

The known polymeric retanning agents for leather are still in need ofimprovement in respect of the body and softness they impart to theleather and in their coloring properties.

It is an object of the present invention, therefore to provide suchretanning agents with corresponding, improved properties.

We have found that this object is achieved by the use of aqueoussolutions or dispersions of copolymers composed of

A) from 5 to 95 mol % of ethylenically unsaturated mono- or dicarboxylicacids having 3 to 10 carbons, their anhydrides, their alkali metal,alkaline earth metal or ammonium salts, or mixtures thereof,

B) from 5 to 95 mol % of ethylenically unsaturated acetals, ketals ororthocarboxylic esters of the formula I ##STR2## where R¹ and R²independently are hydrogen, C₁ -C₁₀ -alkyl, C₁ -C₁₀ -alkoxy, amino, C₁-C₄ -alkylamino or di-C₁ -C₄ -alkylamino,

R³,R⁴,R⁵,R⁶,R⁸,R⁹,R¹⁰ and R¹¹ independently are hydrogen, C₁ -C₁₀-alkoxy, amino, C₁ -C₄ -alkylamino, di-C₁ -C₄ -alkylamino, C₆ -C₁₄-aryl, C₇ -C₁₈ -aralkyl, carboxyl, C₁ -C₂₀ -alkoxycarbonyl, C₂ -C₁₈-alkyl interrupted by 1-5 nonadjacent oxygens, or are sulfo orphosphono,

R⁷ is hydrogen, C₁ -C₁₀ -alkyl, C₆ -C₁₄ -aryl, C₇ -C₁₈ -aralkyl or C₁-C₁₀ -acyl,

R¹² is hydrogen, C₁ -C₁₀ -alkyl, C₁ -C₁₀ -alkoxy, hydroxyl or C₁ -C₁₀-acyloxy and

a,b,c and d independently are 0 or 1, it also being possible for

R² and R⁴ together to form 1,3- or 1,4-alkylene of 3 to 12 carbons andfor

R⁵ and R⁷ together to form 1,2- or 1,3-alkylene of 2 to 12 carbons, and

C) from 0 to 70 mol % of other copolymerizable monomers,

or their hydrolysis products or polymer-analogous reaction products, astanning agents for the self-tanning, pretanning and assist tanning ofleather pelts and skin pelts and for the retanning of leather and skins.

Particularly suitable carboxyl-containing monomers from group A aremonoethylenically unsaturated mono- or dicarboxylic acids or theircorresponding anhydrides of 3 to 6 carbons, for example acrylic,methacrylic, ethylacrylic, allylacetic, crotonic, vinylacetic, maleic,itaconic, mesaconic, fumaric, citraconic, and methylenemalonic acids,monoalkyl maleate, and the alkali, alkaline earth metal and ammoniumsalts of these acids, or mixtures thereof. In the case of monoalkylesters of dicarboxylic acids, the given number of carbons relates to thedicarboxylic acid structure, while the alkyl ester group canindependently have from 1 to 20, especially 1 to 8, carbons. Suitable,corresponding, monoethylenically unsaturated dicarboxylic anhydrides aremaleic anhydride, itaconic anhydride, citraconic anhydride or mixturesthereof. Preference is given to acrylic, methacrylic, maleic anditaconic acid and to maleic anhydride. Group B monomers aremonoethylenically unsaturated acetals, ketals or orthocarboxylic esterswith a cyclic or semicyclic structure.

R¹ and R² independently are preferably hydrogen, C₁ -C₄ -alkyl,especially methyl and ethyl, C₁ -C₄ -alkoxy, especially methoxy andethoxy, N--(C₁ -C₄ -alkyl)amino, especially N-methylamino andN-ethylamino, and N,N-(di-C₁ -C₄ -alkyl)amino, especiallyN,N-dimethylamino and N,N-diethylamino.

R³,R⁴,R⁵,R⁶,R⁸,R⁹,R¹⁰ and R¹¹ independently are preferably hydrogen, C₁-C₄ -alkyl, especially methyl and ethyl, C₁ -C₄ -alkoxy, especiallymethoxy and ethoxy, N--(C₁ -C₄ -alkyl)amino, especially N-methylaminoand N-ethylamino, N,N-(di-C₁ -C₄ -alkyl)amino, especiallyN,N-dimethylamino and N,N-diethylamino, phenyl, tolyl, benzyl, carboxyl,C₁ -C₄ -alkoxycarbonyl, especially methoxycarbonyl and ethoxycarbonyl,and groups of the formula --CH₂ OCH₃, --CH₂ OCH₂ CH₃, --CH₂ CH₂ OCH₃,CH₂ CH₂ OCH₂ CH₃, --CH₂ O(C₂ H₄ O)_(m) CH₃, --CH₂ O(C₃ H₆ O)_(n) CH₃ and--CH₂ O(C₄ H₈ O)_(p) CH₃ (where m, n and p=2 to 4).

R⁷ is preferably hydrogen, C₁ -C₄ -alkyl such as methyl, ethyl,n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl and tert-butyl,phenyl, tolyl, C₇ -C₁₂ -aralkyl such as benzyl and 2-phenylethyl, and C₁-C₄ -acyl such as formyl, acetyl, propionyl and butyryl.

R¹² is preferably hydrogen, C₁ -C₄ -alkyl, such as methyl, ethyl,n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl and tert-butyl, C₁ -C₄-alkoxy such as methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy,isobutoxy, sec-butoxy and tert-butoxy, hydroxyl and C₁ -C₄ -acyloxy,such as acetoxy, propionyloxy and butyryloxy. R¹² is particularlypreferably hydrogen.

1,3- or 1,4-alkylene formed jointly by R² and R⁴ is, in particular,--CH₂ CH₂ CH₂ --, --CH(CH₃)CH₂ CH₂ --, --CH(CH₃)CH₂ CH(CH₃)--, --CH₂CH(CH₃)CH₂ --, --CH(C₄ H₉)CH₂ CH₂ --, --CH₂ CH₂ CH₂ CH₂ --, --CH(CH₃)CH₂CH₂ CH₂ -- and --CH(C₄ H₉)CH₂ CH₂ CH₂ --.

1,2- or 1,3-alkylene formed jointly by R⁵ and R⁷ is, in particular,--CH₂ CH₂ --, --CH(CH₃)CH₂ --, --CH(CH₃)CH(CH₃)--, --CH(C₂ H₅)CH₂ --,--CH(C₄ H₉)CH₂ --, --CH₂ CH₂ CH₂ --, --CH(CH₃)CH₂ CH₂ --, --CH(CH₃)CH₂CH(CH₃)--, --CH₂ CH(CH₃)CH₂ -- and --CH(C₄ H₉)CH₂ CH₂ --.

In a preferred embodiment, the monomers B copolymerized are5,6-dihydro-4H-pyrans of the formula Ia ##STR3## (R³ and R⁶ =hydrogen, aand b=1, c and d=0) or 2,5-dihydrofurans of the formula Ib ##STR4## (R¹and R² =hydrogen, a, b and d=0, c 1) the variables in formulae Ia and Ibbeing as defined above.

Specific examples of monomers B are: ##STR5##

Especially preferred monomers B are: ##STR6##

Examples of the preferably carboxyl-free group C monomers include:

C₁ -C₃₀ esters of acrylic or methacrylic acid, for example methyl,ethyl, propyl, isopropyl, butyl, hexyl, 2-ethylhexyl, lauryl andoctadecyl (meth)acrylate and phenoxyethyl acrylate;

hydroxyalkyl esters of acrylic or methacrylic acid, for examplehydroxyethyl and hydroxypropyl (meth)acrylate and 1,4-butanediolmonoacrylate;

alkyloxyalkyl esters of monoethylenically unsaturated C₃ -C₁₀ -mono- or-dicarboxylic acids, for example methyldiglycol acrylate andmethylpentaglycol methacrylate;

diesters of maleic acid, for example dimethyl and dibutyl maleate;

linear and branched-chain α-olefins or mixtures thereof, such as ethene,propene, butene, isobutene, pentene, cyclopentene, hexene, cyclohexene,octene and 2,4,4-trimethyl-1-pentene as a mixtures, if desired, with2,4,4-trimethyl-2-pentene, 1-octene, C₈ -C₁₀ olefin, 1-dodecene, C₁₂-C₁₄ olefin, C₂₀ -C₂₄ olefin; oligoolefins prepared under metallocenecatalysts, such as oligopropene, oligohexene and oligooctadecene; andolefins prepared by cationic polymerization and having a high α-olefincontent, for example reactive polyisobutene;

acrylamides and alkyl-substituted acrylamides, for example acrylamide,methacrylamide and N-tert-butylacrylamide;

vinyl and allyl alkyl ethers of 1 to 40 carbons in the alkyl radical,which radical can also carry further substituents such as hydroxyl,amino or dialkylamino or one or more alkoxylate groups, examples being:methyl, ethyl, propyl, isobutyl, 2-ethylhexyl, decyl, dodecyl,octadecyl, 2-(diethylamino)ethyl, 2-(di-n-butyl-amino)ethyl andmethyldiglycol vinyl ethers and the corresponding allyl ethers;

sulfo-containing monomers, for example allylsulfonic andmethallylsulfonic acid, styrene sulfonate, vinylsulfonic acid,allyloxybenzenesulfonic acid and 2-acrylamido-2-methylpropanesulfonicacid;

acrylamides or (meth)acrylates, containing tertiary amino, such as2-(N,N-dimethylamino)ethyl (meth)acrylate, 2-(N,N-diethylamino)ethyl(meth)acrylate, 2-dimethylaminoethyl(meth)acrylamide and3-dimethylaminopropyl(meth)acrylamide, and their salts with mineralacids or their quaternization products with alkyl halides or alkylsulfates;

vinyl esters of C₁ -C₂₀ -carboxylic acids, for example vinyl formate,acetate, propionate, butyrate, stearate and laurate;

N-vinylcarboxamides of C₁ -C₈ carboxylic acids, for exampleN-vinylformamide, N-vinyl-N-methylformamide and N-vinylacetamide;

other comonomers, for example styrene, α-methylstyrene, butadiene,N-vinylpyrrolidone, N-vinylimidazole, acrolein, methacrolein,acrylonitrile, 4-vinylpyridine, indene and diallyldimethylammoniumchloride.

Preferred group C comonomers are methyl (meth)acrylate, ethyl(meth)acrylate, lauryl (meth)acrylate, butene, isobutene,2,4,4-trimethyl-1-pentene, 1-octene, C₈ -C₁₀ olefin, 1-dodecene, C₁₂-C₁₄ olefin, C₂₀ -C₂₄ olefin, oligopropene, oligohexene,oligooctadecene, reactive polyisobutene, vinyl stearate,2-acrylamido-2-methylpropanesulfonic acid, ethylhexyl vinyl ether,styrene, acrolein and acrylonitrile.

The group A and C monomers are very common polymer structural units andare readily available.

The group B monomers of formula I can be prepared by various methods,examples being: preparation from halogen/Oalkyl acetals with alcohols,preparation from aldehydes or ketones with hydroxy compounds,preparation from enol ethers with alcohols, preparation from enones andenol ethers by [4+2] cycloaddition or from ethers by electrolysis. Theseand other methods are compiled in general form, for example, inHouben-Weyl, Methoden der Organischen Chemie, Vol. E14a/1, Ed. H.Hagemann, Thieme-Verlag 1991.

In J. Pol. Sci., Part A, Polymer Chemistry, Vol. 28, (1990) 2719-2728(3) M. J. Han et al. describe copolymers of maleic anhydride with5,6-dihydro-4H-pyran and various of its derivatives, for example6-methoxy-5,6-dihydro-4H-pyran, 6-ethoxy-5,6-dihydro-4H-pyran,6-acetoxy-5,6-dihydro-4H-pyran and 6-hydroxy-5,6-dihydro-4H-pyran.Copolymerization is performed at 70° C. in acetone using2,2'-azobis(isobutyronitrile) as initiator. The polymers are obtained inyields of 20 and 72%. The copolymers were tested for their effectivenessagainst tumor cells.

The novel copolymers described are composed preferably of from 10 to 90mol % of monomers A and from 10 to 90 mol % of monomers B. If monomers Care included, then their proportion is preferably from 10 to 70 mol %.

The polymerization can be carried out in the presence of inert solventsor inert diluents or else in their absence, as a bulk polymerization.The use of solvents or diluents has the advantages of ensuring both gooddissipation of the heat of polymerization and a low viscosity. Solventswhich can be employed are those capable of dissolving both the monomersand the polymer which is formed. This is called solution polymerization.The method or precipitation polymerization can also be employed toadvantage, where the monomers are at least partially soluble in thesolvent but the polymer which forms is not. Consequently, the product isprecipitated as the polymerization progresses. This ensures a lowviscosity during polymerization and makes it easy to isolate the solidproduct if desired. Other polymerization techniques which can be used toadvantage to prepare the copolymers described are emulsion andsuspension polymerization. In these cases the monomers are distributedin dispersed form in a continuous phase--usually water, althoughhydrocarbons or other solvents can also be used. The advantages of suchmethods are that polymerization can be carried out at low viscosity andthat the products, especially when water is used as continuous phase,can in most cases be employed directly for their intended application.

In the case of precipitation, suspension or emulsion polymerization itmay be advantageous to use emulsifiers or protective colloids in orderto stabilize the droplets or particles. Examples of emulsifiers are:alkylphenol ethoxylates, primary alcohol ethoxylates, linearalkylbenzenesulfonates, alkyl sulfates, ethylene oxide/propylene oxideblock copolymers or alkyl polyglucosides.

Examples of protective colloids are cellose derivatives, polyethyleneglycol, polypropylene glycol, copolymers of ethylene glycol andpropylene glycol, polyvinyl acetate, polyvinyl alcohol, polyvinyl ether,starch and starch derivatives, dextran, polyvinylpyrrolidone,polyvinylpyridine, polyethyleneimine, polyvinylimidazole,polyvinylsuccinimide, polyvinyl-2-methylsuccinimide,polyvinyl-1,3-oxazolid-2-one, polyvinyl-2-methylimidazoline andcopolymers containing maleic acid and/or maleic anhydride. Theemulsifiers or protective colloids are usually used in concentrations offrom 0.05 to 15% by weight, based on the monomers.

The polymers described are preferably prepared by the method ofprecipitation or solution polymerization. Examples of suitable solventsand diluents are toluene, o-xylene, p-xylene, ethylbenzene, industrialmixtures of alkyl aromatic compounds, cyclohexane, industrial mixturesof aliphatic compounds, acetone, cyclohexanone, tetrahydrofuran,dioxane, glycols and glycol derivatives, polyalkylene glycols and theirderivatives, diethyl ether, tert-butyl methyl ether, methyl acetate,ethanol, isopropanol and water and mixtures of different solvents, forexample water/isopropanol or isopropanol/diethylene glycol. If water isused there is a risk of some of the ethylenically unsaturated acetalemployed hydrolyzing before it can be incorporated by polymerization.This can be prevented by carrying out polymerization in a pH range whichdoes not permit hydrolysis to occur. This range is situated above a pHof 3. If carboxyl- or sulfo-containing monomers are used in aqueoussolution, they are preferably in partly neutralized form in order tosafeguard the correct pH range. Furthermore, a buffer system can also beused.

Polymerization can be carried out continuously or batchwise, at from 20°C. to 250° C., preferably 50° C. to 160° C. Polymerization is preferablycarried out by metering at least part of the monomers and of theinitiator into the reaction vessel during polymerization and making thefeed time as long as is desired so as to release the heat given off inpolymerization over a defined period. The inflow of monomers into thereactor per unit time can be kept constant; however, it is also possibleto alter the flow of monomers and/or initiator during the polymerizationin order, for example to obtain a certain molecular weight distributionor to bring about altered copolymer compositions.

The copolymers described are generally prepared using initiators whichform free radicals. Suitable such free-radical initiators are preferablyall those compounds which at the particular polymerization temperaturechosen have a half life of from 1 minute to 10 hours. If polymerizationis begun at a lower temperature and completed at a higher temperature,it is advantageous to operate with at least two initiators decomposingat different temperatures, ie. an initiator which decomposes at thelower temperature, to initiate polymerization, and then an initiatorwhich decomposes at the higher temperature, in order to complete themain polymerization. The initiator used is generally soluble in therespective solvent or diluent. In the case of polymerization in dispersephase, it is also possible to employ initiators soluble only in onephase.

It is common to employ peroxides or azo compounds as polymerizationinitiators, eg. acetyl cyclohexanesulfonyl peroxide, diacetylperoxydicarbonate, dicyclohexyl peroxydicarbonate, di-2-ethylhexylperoxydicarbonate, tert-butyl perneodecanoate,2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile),2,2'-azobis(2-methyl-N-phenylpropionamidine)dihydrochloride, tert-butylperpivalate, dioctanoyl peroxide, dilauroyl peroxide,2,2'-azobis(2,4-dimethylvaleronitrile), dibenzoyl peroxide, tert-butylper-2-ethylhexanoate, tert-butyl permaleate,2,2'-azobis(isobutyronitrile), dimethyl 2,2'-azobisisobutyrate, sodiumpersulfate, potassium persulfate, ammonium persulfate, bis(tert-butylperoxy)cyclohexane, tert-butyl peroxyisopropylcarbonate, tert-butylperacetate, hydrogen peroxide, 2,2-bis(tert-butylperoxy)butane, dicumylperoxide, di-tert-amyl peroxide, di-tert-butyl peroxide, pinanehydroperoxide or tert-butyl hydroperoxide.

The half lives of the abovementioned free-radical initiators can bereduced by additionally using salts or complexes of heavy metals, forexample salts of copper, cobalt, manganese, iron, vanadium, cerium,nickel or chromium, or organic compounds such as benzoin,dimethylaniline or ascorbic acid. For example, tert-butyl hydroperoxidecan be activated by the addition of 5 ppm of copper(II) acetylacetonatesuch that polymerization can be carried out at as low as 100° C. Thereducing component of redox catalysts can also be formed, for example,by compounds such as sodium sulfite, sodium bisulfite, sodiumformaldehyde-sulfoxylate and hydrazine.

Based on the monomers employed in polymerization, from 0.01 to 20% byweight, preferably from 0.05 to 15% by weight, of a polymerizationinitiator or mixture of two or more such initiators is used. As redoxcomponents, from 0.01 to 30% by weight of the reducing compounds isadded. Heavy metals are employed in a proportion ranging from 0.1 to 100ppm, preferably from 0.5 to 10 ppm. It is often advantageous to use acombination of peroxide, reducing agent and heavy metal as redoxcatalyst.

To prepare polymers of low average molecular weight, polymerization isadvantageously carried out in the presence of regulators, examples ofsuitable such regulators being mercapto compounds, such asmercaptoethanol, mercaptopropanol, mercaptobutanol, mercaptoacetic acid,mercaptopropionic acid, butylmercaptan, n-dodecylmercaptan ortert-dodecylmercaptan. Other suitable regulators are allyl alcohol,propionaldehyde, n-butyraldehyde and isobutyraldehyde, formic acid,ammonium formate, propionic acid, hydrazine sulfate, hydroxylammoniumsulfate and butenols. If used, the required amount of regulator is from0.05 to 20% by weight, based on the monomers used in polymerization. Thecopolymers have a number-average molecular weight of from 500 to1,000,000, preferably from 800 to 150,000.

If polymerization is carried out in bulk, then in order to obtain auseful product the polymer must be converted to an aqueous solution ordispersion. This can be done, for example, by adding water to thepolymer after the end of the polymerization and dissolving or dispersingthe mixture at an appropriate temperature. If desired, the polymer canalso be introduced as a melt or solid, with stirring, into a stirredvessel filled with water.

Any organic solvent or precipitating agent used during thepolymerization must be substantially removed and replaced by water inorder to obtain a useful product. In the case of a precipitationpolymerization, an option is to isolate the polymer by drying,filtration or distillative removal of the solvent and then to treat itwith water. It is often advantageous to use a steam-volatile solvent forthe polymerization, which provides the option of removing the solvent bysteam distillation. The technique of steam distillation can also be usedadvantageously following solution polymerization in a steam-volatilesolvent, in which case the use of an antifoam or foam suppressant may beadvantageous.

The cyclic and semicyclic acetals copolymerized as monomers B can behydrolyzed, in a polymer-analogous reaction, to the correspondingaldehydes. Furthermore, the copolymerized ketals or orthocarboxylicesters can be converted into the corresponding ketones or, respectively,carboxylic acids. The presence of free or hydrated aldehyde, ketone orcarboxyl groups in the polymers may increase both the water-solubilityof the products and their efficiency. To promote the formation ofaldehyde, ketone or orthocarboxylic acid groups, the aqueous polymersolution or dispersion is heated for a relatively long period.Substantial hydrolysis of the acetal groups takes place, in particular,in the course of steam distillation in an acid medium. To accelerate theprocess of hydrolysis, it is also possible to employ a catalyst, forexample p-toluenesulfonic acid, as well. In principle, under theseconditions of hydrolysis, carboxylic anhydride structures of themonomers A may also be converted into carboxyl.

The aldehyde group-containing polymers obtained after opening theacetals may be subjected to further polymer-analogous reaction. Forexample, they can be reacted with alcohols to give hemiacetals oracetals, with mercaptans to give thioacetals, with ammonia or primaryamines to give Schiff bases, with hydroxylamines to give oximes, withhydrazines to give hydrazones, with secondary amines to give enaminesand with sodium bisulfite to give bisulfite addition compounds. Thealdehyde groups can also be reduced to alcohols or amines. Similarly,ketone or carboxyl groups obtainable by hydrolysis can be subjected topolymer-analogous reactions in accordance with techniques known per se.

If the group A comonomer used comprises a monoethylenically unsaturateddicarboxylic anhydride, such as maleic anhydride, then the anhydridegroup can be reacted in a polymer-analogous way provided thepolymerization was not carried out in a nonaqueous medium where,consequently, the anhydride group was not hydrolyzed. To bring aboutpartial esterification of the anhydride groups present in the copolymer,they are reacted with alcohols, using quantities of alcohols such that10 to 70% of the total carboxyls resulting from the copolymerizeddicarboxylic anhydride fractions are esterified. This esterificationtakes place preferably with the exclusion of water. Suitable alcoholsmay contain 1 to 40, preferably 3 to 30, carbons, and may be primary,secondary or tertiary.

In this context it is possible to use both saturated aliphatic alcoholsand unsaturated alcohols, for example oleyl alcohol. It is preferred touse monohydric, primary or secondary alcohols, eg. methanol, ethanol,n-propanol, isopropanol, n-butanol, isobutanol, n-pentanol and isomers,n-hexanol and isomers, n-octanol and isomers, such as 2-ethylhexanol;nonanols, decanols, dodecanols, tridecanols, cyclohexanol, tallow fattyalcohol, stearyl alcohol, alkoxylated C₁ -C₃₀ -alcohols, for examplemethyldiglycol and methylpentaglycol, or polyalkylene glycols, forexample polyethylene glycol, polypropylene glycol andpolytetrahydrofuran, and also the alcohols or alcohol mixtures of 9 to19 carbons which are readily obtainable industrially by oxo synthesis,for example C_(9/11) oxo alcohol, C_(13/15) oxo alcohol, and alsoZiegler alcohols of 12 to 24 carbons. Preference is given to the use ofC₃ -C₃₀ alcohols such as n-butanol, isobutanol, amyl alcohol,2-ethylhexanol, tridecanol, tallow fatty alcohol, stearyl alcohol,C_(9/11) oxo alcohol, C_(13/15) oxo alcohol, C_(12/14) Alfols® andC_(16/18) Alfols. Esterification can if desired be accelerated by theuse of a catalyst such as p-toluenesulfonic acid, for example.

The copolymers containing anhydride groups can also be amidated orimidized by addition of primary or secondary amines, respectively.Amidation/imidization is carried out using quantities of amines suchthat from 10 to 70% of the total carboxyls formed from the copolymerizeddicarboxylic anhydride fractions are amidated or from 10 to 70% of thecopolymerized dicarboxylic anhydride units are imidized.

To form amides ammonia and primary and secondary amines can be used.Amide formation takes place preferably in the absence of water byreaction of the anhydride groups of the copolymer with ammonia or withthe amines. The primary and secondary amines which are relevant maycontain 1 to 40, preferably 3 to 30 carbons. Suitable examples aremethylamine, ethylamine, n-propylamine, isopropylamine, n-butylamine,isobutylamine, hexylamine, cyclohexylamine, methylcyclohexylamine,2-ethylhexylamine, n-octylamine, isotridecylamine, tallow fatty amine,stearylamine, oleylamine, dimethylamine, diethylamine, di-n-propylamine,diisopropylamine, di-n-butylamine, diisobutylamine, dihexylamine,dicyclohexylamine, dimethylcyclohexylamine, di-2-ethylhexylamine,di-n-octylamine, diisotridecylamine, di-tallow fatty amine,distearylamine, dioleylamine, ethanolamine, diethanolamine,n-propanolamine, di-n-propanolamine, sarcosine, taurine and morpholine.By selecting appropriate reaction conditions, ammonia or primary aminescan be used to produce imide structures from the dicarboxylic anhydrideunits of the copolymer.

Following partial conversion of the anhydride groups to monoester,monoamide or imide groups and, if desired, subsequent hydrolytic openingof the acetal, ketal or ortho-ester groups, the remaining anhydridegroups of the polymer can be hydrolyzed. This can also be carried outsimultaneously with the partial neutralization which is still necessary,by adding an aqueous base to the partially esterified, amidated orimidized copolymer which still contains anhydride groups. To acceleratehydrolysis of the anhydride groups it is also possible if desired to addan appropriate catalyst, such as 4-dimethylaminopyridine.

The carboxyl-containing copolymers are generally converted to aneutralized form. Preferably, 10-95% of the carboxyls are neutralized.Examples of suitable neutralizing bases are alkali metal or alkalineearth metal hydroxides, for example sodium hydroxide, potassiumhydroxide or magnesium hydroxide, alkali metal or alkaline earth metalcarbonates, for example sodium carbonate or potassium carbonate,ammonia, methylamine, dimethylamine, trimethylamine, ethylamine,diethylamine, triethylamine, ethanolamine, diethanolamine,dimethylethanolamine, triethanolamine or morpholine. Neutralization cantake place either during actual polymerization, for example by employingpartially neutralized monomers, or following polymerization and, ifdesired, after the hydrolytic opening of the acetal, ketal ororthocarboxylic ester structures.

The copolymer solutions or dispersions obtainable in this way are highlysuitable as tanning agents in the production of leather and furs. Forinstance, the copolymers used in accordance with the invention can beused for the self-tanning and pretanning of leather pelts and skin peltsin aqueous liquor. In this case an advantageous procedure is to treatthe pickled leather pelts, for example cattle pelts having a splitthickness of from 1.5 to 4 mm, or skin pelts, for example sheepskinpelts, with an aqueous solution or dispersion of the copolymers used inaccordance with the invention at a pH from 2 to 7, in particular from2.5 to 4.5, and at from 15 to 40° C., in particular from 20 to 35° C.,for a period of from 2 to 20 hours. This treatment takes the form, forexample, of milling in a drum. The required quantity of copolymers usedin accordance with the invention is normally, based on the weight ofpelt, from 2 to 30% by weight, in particular from 5 to 25% by weight.The liquor length, ie. the percentage ratio of treatment liquor togoods, is customarily from 30 to 200% in the case of leather pelts andfrom 100 to 2000% in the case of skin pelts, based in each case on thepelt weight.

On completion of the treatment the leather or skin is customarilybrought to a pH of from 2 to 8, in particular from 3 to 5, using forexample magnesium oxide, sodium carbonate, sodium bicarbonate or anorganic acid, such as formic acid, or a salt thereof, is treated ifdesired with further tanning agents, and, toward the end or oncompletion of the tanning process, is optionally dyed and fatliquored.

The copolymers used in accordance with the invention can additionally beused for assist tanning of leather pelts and skin pelts together withthe tanning agents of the main tannage, which may for example be achrome, aluminum, titanium or zirconium tannage. In this case theworking conditions concerning pH, temperature and duration of treatmentare adjusted to the requirements of the main components of the tanning;the same applies to the treatment apparatus, the liquor length and theaftertreatment. In this case the requisite quantity of copolymer used inaccordance with the invention is normally, based on the leather peltweight, from 0.1 to 20% by weight, in particular from 0.5 to 14% byweight.

The copolymers used in accordance with the invention can also beemployed for retanning previously tanned leather and skin, for examplechrome tanned leather (wet blue), wet white (ie. leather pelts or skinpelts pretanned with, for example, aldehydes or syntans) orvegetable-tanned leather or skin, working in an aqueous liquor.Preferably, chrome-tanned leather is retanned. This is generally carriedout by tanning the pickled leather pelts and skins, for example cattlepelts having split thicknesses of from 1.5 to 4 mm, with, for example, acustomary chromium-containing tanning agent such as a chromium(III)salt, eg. chromium(III) sulfate, in a conventional manner, deacidifyingthe resulting pretanned hides, and treating the deacidified hides at apH of from 2 to 7, in particular from 2.5 to 6, and at from 15 to 60°C., in particular from 25 to 45° C., with an aqueous solution ordispersion of the copolymers used in accordance with the invention, fora period of from 0.25 to 12 hours. This treatment takes the form, forexample, of milling in a drum. The required quantity of copolymer usedin accordance with the invention is normally, based on the shaved weightof the leather, from 2 to 30% by weight, in particular from 5 to 25% byweight. The liquor length is normally from 30 to 200% in the case ofleather pelts and from 100 to 2000% in the case of skin pelts, based ineach case on the shaved weight of the leather.

After the treatment, and if necessary beforehand as well, the leather orskin is customarily adjusted to a pH of from 3 to 5, for example usingmagnesium oxide or an organic acid, such as formic acid, or saltsthereof, and toward the end of or after the treatment it is, if desired,dyed and fatliquored.

The leather or skin which has been retanned in this way may have beenadditionally treated, prior to retanning with the copolymers used inaccordance with the invention, with other tanning agents, such aspolymer tanning agents, syntans or vegetable tanning agents. Moreover,the copolymers used in accordance with the invention may be employed atthe same time as such additional tanning agents.

Suitable tanning agents used in addition or simultaneously are allcustomary agents having a tanning action on leather pelts and skinpelts. A comprehensive treatment of such tanning agents may be found,for example, in Ullmanns Enzyklopadie der technischen Chemie, 3rdEdition, Volume 11, (1960) pp.585-612. Specific classes of tanning agentwhich may be mentioned are the mineral tanning agents, for examplechromium, aluminum, titanium and zirconium salts, the synthetic tanningagents (syntans), vegetable (plant-derived) tanning agents, and polymertanning agents.

The leather produced with the copolymers used in accordance with theinvention shows outstanding results in respect of light fastness andthermal stability. This is observed in particular on chrome-pretannedleather. Moreover, even at low rates of application, the copolymers usedin accordance with the invention provide very good body, great softnessand good firm grain. At high rates, there is no hardening of theleather.

Surprisingly, the disadvantageous dyeing behavior of polymers based onacrylic and methacrylic acid is no longer found with the copolymers usedin accordance with the invention. The latter products, for instance,give rise to leather having a very dark coloration and enhancedthrough-coloring, and at the same time very uniform and level dyeingsare achieved.

A particular advantage of the copolymers used in accordance with theinvention is that, unlike conventional syntans, they contain nohealth-endangering unsulfonated phenols as residual monomers, and, incomparison to conventional polymer tanning agents, the increasedreactivity of the latent aldehyde functions present in the copolymermeans that better exhaustion of the tanning liquors is achieved, withthe result that a lesser degree of pollution of the wastewaters withorganic substances is observed.

Since some of the copolymers described are novel, the present inventionadditionally provides copolymers composed of

A) from 5 to 95 mol % of ethylenically unsaturated mono- or dicarboxylicacids having 3 to 10 carbons, their anhydrides, their alkali metal,alkaline earth metal or ammonium salts, or mixtures thereof,

B) from 5 to 95 mol % of ethylenically unsaturated acetals, ketals ororthocarboxylic esters of the formula I ##STR7## where R¹ and R²independently are hydrogen, C₁ -C₁₀ -alkyl, C₁ -C₁₀ -alkoxy, amino, C₁-C₄ -alkylamino, or di-C₁ -C₄ -alkylamino,

R³,R⁴,R⁵,R⁶,R⁸,R⁹,R¹⁰ and R¹¹ independently are hydrogen, C₁ -C₁₀-alkoxy, amino, C₁ -C₄ -alkylamino, di-C₁ -C₄ -alkylamino, C₆ -C₁₄-aryl, C₇ -C₁₈ -aralkyl, carboxyl, C₁ -C₂₀ -alkoxycarbonyl, C₂ -C₁₈-alkyl interrupted by 1-5 nonadjacent oxygens, or are sulfo orphosphono,

R⁷ is hydrogen, C₁ -C₁₀ -alkyl, C₆ -C₁₄ -aryl, C₇ -C₁₈ -aralkyl or C₁-C₁₀ -acyl,

R¹² is hydrogen, C₁ -C₁₀ -alkyl, C₁ -C₁₀ -alkoxy, hydroxyl or C₁ -C₁₀-acyloxy and

a,b,c and d independently are 0 or 1, it also being possible for

R² and R⁴ together to form 1,3- or 1,4-alkylene of 3 to 12 carbons andfor

R⁵ and R⁷ together to form 1,2- or 1,3-alkylene of 2 to 12 carbons, and

C) from 0 to 70 mol % of other copolymerizable monomers,

with the exception of those whose copolymerized monomer A comprisesmaleic anhydride and whose copolymerized monomer B comprises6-acetoxy-5,6-dihydro-4H-pyran, 6-methoxy-5,6-dihydro-4H-pyran,6-ethoxy-5,6-dihydro-4H-pyran or 6-hydroxy-5,6-dihydro-4H-pyran,

and hydrolysis products and polymer-analogous reaction products of thesecopolymers.

The disclaimed copolymers of maleic anhydride and the fourabovementioned monomers B are already known from (3), where, however,they are recommended for an entirely different use.

EXAMPLES

Unless otherwise stated, percentages are by weight.

The K values of the copolymers were determined by the method of H.Fikentscher, Cellulose-Chemie, Volume 13, (1932) 58-64 and 71-74 in anaqueous solution of the sodium salts of the copolymers at aconcentration of 1% by weight, at a pH of 7 and at 25° C.

The solids contents were determined by drying for 2 hours at 80° C.under reduced pressure.

Preparation of the copolymers

Example 1

A stirred 4 l glass reactor fitted with anchor stirrer, 2 automatic feedmetering devices, reflux condenser and oil-bath heating was charged with147.0 g of maleic anhydride and 1178 g of toluene, and these componentswere heated to 110° C. under inert gas. Feed stream 1, consisting of171.0 g of 6-methoxy-5,6-dihydro-4H-pyran, was metered at a uniform rateover 3 hours into the resulting solution. Beginning at the same time asfeed stream 1, feed stream 2, consisting of 22.6 g of tert-butylper-2-ethylhexanoate and 94 g of toluene, was metered in at a uniformrate over the course of 4 hours. Subsequently, the reaction mixture waspost-polymerized at 110° C. for 2 hours more. After the end ofpolymerization, a pale brown suspension of low viscosity was obtained.200 g of deionized water were added to the reaction mixture, and theorganic solvent was distilled off azeotropically by passing in steam. Atthe end of steam distillation a brown solution was present, which wascooled and neutralized with 154.0 g of 50% sodium hydroxide solution.This gave a dark brown, clear solution with a pH of 7.2 and a solidscontent of 33.4%. The K value of a 1% strength aqueous solution of thecopolymer (pH 7) was 15.0.

Example 2

A stirred 4 l glass reactor fitted with anchor stirrer, 2 automatic feedmetering devices, reflux condenser and oil-bath heating was charged with147.0 g of maleic anhydride and 1178 g of toluene, and these componentswere heated to 110° C. under inert gas. Feed stream 1, consisting of171.0 g of 6-methoxy-5,6-dihydro-4H-pyran, was metered at a uniform rateover 3 hours into the resulting solution. Beginning at the same time asfeed stream 1, feed stream 2, consisting of 22.6 g of tert-butylper-2-ethylhexanoate and 94 g of toluene, was metered in at a uniformrate over the course of 4 hours. Subsequently, the reaction mixture waspost-polymerized at 110° C. for 2 hours more. After the end ofpolymerization, a pale brown suspension of low viscosity was obtained.200 g of deionized water were added to the reaction mixture, and theorganic solvent was distilled off azeotropically by passing in steam. Atthe end of steam distillation a brown solution was present, which wastreated with 0.32 g of p-toluenesulfonic acid, stirred at 100° C. for anhour, then cooled and neutralized with 154.0 g of 50% sodium hydroxidesolution. This gave a black-brown, clear solution with a pH of 7.2 and asolids content of 33.6%. The K value of a 1% strength aqueous solutionof the copolymer (pH 7) was 15.0.

Example 3

A stirred 4 l glass reactor fitted with anchor stirrer, 2 automatic feedmetering devices, reflux condenser and oil-bath heating was charged with147.0 g of maleic anhydride and 1178 g of o-xylene, and these componentswere heated to 145° C. under inert gas. Feed stream 1, consisting of171.0 g of 6-methoxy-5,6-dihydro-4H-pyran, was metered at a uniform rateover 3 hours into the resulting solution. Beginning at the same time asfeed stream 1, feed stream 2, consisting of 22.3 g of tert-butylper-2-ethylhexanoate and 94 g of o-xylene, was metered in at a uniformrate over the course of 4 hours. Subsequently, the reaction mixture waspost-polymerized at 145° C. for 2 hours more. After the end ofpolymerization, a brown suspension of low viscosity was obtained. 200 gof deionized water were added to the reaction mixture, and the solvent,o-xylene, was distilled off azeotropically by passing in steam. At theend of steam distillation a brown solution was present, which was cooledand neutralized with 120.0 g of 50% sodium hydroxide solution. This gavea dark brown, clear solution with a pH of 7.1 and a solids content of41.0%. The K value of a 1% strength aqueous solution of the copolymer(pH 7) was 12.2.

Example 4

A stirred 4 1 glass reactor fitted with anchor stirrer, 2 automatic feedmetering devices, reflux condenser and oil-bath heating was charged with200.0 g of 6-methoxy-5,6-dihydro-4H-pyran and 1350 g of toluene, andthese components were heated to 110° C. under inert gas. Feed stream 1,consisting of 200.0 g of methacrylic acid, was metered at a uniform rateover 2 hours into the resulting solution. Beginning at the same time asfeed stream 1, feed stream 2, consisting of 4.0 g of2,2'-azoisobutyronitrile and 250 g of toluene, was metered in at auniform rate over the course of 3 hours. Subsequently, the reactionmixture was post-polymerized at 110° C. for 1.5 hours more. Thesuspended solid product was filtered off and washed with toluene. Thepale yellowish powder was dried under reduced pressure, to give 234 g ofthe copolymer.

For conversion to an aqueous solution, 90.0 g of the copolymer wereplaced with 360 g of deionized water into a 2 l glass reactor fittedwith steam inlet pipe and Liebig condenser, and were slowly heated to10° C. Steam was passed through the mixture for 4 h. A pale brownish,cloudy solution with a pH of 3.0 and a solids content of 9.3% wasobtained. The K value of a 1% strength aqueous solution of the copolymeradjusted to a pH of 7 using sodium hydroxide was 46.9.

Example 5

A stirred 2 l glass reactor fitted with anchor stirrer, 2 automatic feedmetering devices, reflux condenser and oil-bath heating was charged with40.0 g of 6-methoxy-5,6-dihydro-4H-pyran and 600 g of o-xylene, andthese components were heated to 90° C. under inert gas. Feed stream 1,consisting of 160.0 g of methacrylic acid and 100 g of o-xylene, wasmetered at a uniform rate over 2 hours into the resulting solution.Beginning at the same time as feed stream 1, feed stream 2, consistingof 4.0 g of tert-butyl per-2-ethylhexanoate and 100 g of o-xylene, wasmetered in at a uniform rate over the course of 3 hours. Subsequently,the reaction mixture was post-polymerized at 90° C. for 1.5 hours more.After separating off the solvent in a rotary evaporator, 205.0 g of thecopolymer were obtained in the form of a fine white powder.

For conversion to an aqueous solution, 175.0 g of the copolymer wereplaced with 525 g of deionized water into a 2 l glass reactor fittedwith Liebig condenser, and were slowly heated to 100° C. Nitrogen waspassed through the mixture for 30 minutes and residues of o-xylene wereremoved by distillation. The mixture was cooled to 50° C. andneutralized by slow addition of 120.0 g of 50% sodium hydroxidesolution. A yellow, cloudy solution with a pH of 7.15 and a solidscontent of 25.0% was obtained. The K value of a 1% strength aqueoussolution of the copolymer (pH 7) was 61.4.

Example 6

A stirred 2 l glass reactor fitted with anchor stirrer, 2 automatic feedmetering devices, reflux condenser and oil-bath heating was charged with26.1 g of 6-methoxy-5,6-dihydro-4H-pyran and 600 g of o-xylene, andthese components were heated to 90° C. under inert gas. Feed stream 1,consisting of 173.9 g of methacrylic acid and 100 g of o-xylene, wasmetered at a uniform rate over 2 hours into the resulting solution.Beginning at the same time as feed stream 1, feed stream 2, consistingof 4.0 g of tert-butyl per-2-ethylhexanoate and 100 g of o-xylene, wasmetered in at a uniform rate over the course of 3 hours. Subsequently,the reaction mixture was post-polymerized at 90° C. for 1.5 hours more.After separating off the solvent in a rotary evaporator, 217.0 g of thecopolymer were obtained in the form of a fine white powder.

For conversion to an aqueous solution, 195.0 g of the copolymer wereplaced with 550 g of deionized water into a 2 l glass reactor fittedwith Liebig condenser, and were slowly heated to 100° C. Nitrogen waspassed through the mixture for 40 minutes and residues of o-xylene wereremoved by distillation. The mixture was diluted with 200 g of deionizedwater, cooled to 50° C. and neutralized by slow addition of 135.0 g of50% sodium hydroxide solution. A yellow, cloudy solution with a pH of7.15 and a solids content of 24.4% was obtained. The K value of a 1%strength aqueous solution of the copolymer (pH 7) was 66.3.

Example 7

A stirred 2 l glass reactor fitted with anchor stirrer, 2 automatic feedmetering devices, reflux condenser and oil-bath heating was charged with40.0 g of 6-methoxy-5,6-dihydro-4H-pyran and 600 g of o-xylene, andthese components were heated to 110° C. under inert gas. Feed stream 1,consisting of 160.0 g of methacrylic acid and 100 g of o-xylene, wasmetered at a uniform rate over 2 hours into the resulting solution.Beginning at the same time as feed stream 1, feed stream 2, consistingof 4.0 g of tert-butyl per-2-ethylhexanoate and 100 g of o-xylene, wasmetered in at a uniform rate over the course of 3 hours. Subsequently,the reaction mixture was post-polymerized at 110° C. for 1.5 hours more.After separating off the solvent in a rotary evaporator, 206.0 g of thecopolymer were obtained in the form of a fine white powder.

For conversion to an aqueous solution, 170.0 g of the copolymer wereplaced with 510 g of deionized water into a 2 l glass reactor fittedwith Liebig condenser, and were slowly heated to 100° C. Nitrogen waspassed through the mixture for 45 minutes and residues of o-xylene wereremoved by distillation. The mixture was cooled to 50° C. andneutralized by slow addition of 115.0 g of 50% sodium hydroxidesolution. A yellow, cloudy solution with a pH of 7.15 and a solidscontent of 27.2% was obtained. The K value of a 1% strength aqueoussolution of the copolymer (pH 7) was 46.4.

Example 8

A stirred 4 l glass reactor fitted with anchor stirrer, 2 automatic feedmetering devices, reflux condenser and oil-bath heating was charged with147.0 g of maleic anhydride and 1178 g of toluene, and these componentswere heated to reflux under inert gas. Feed stream 1, consisting of171.0 g of 6-methoxy-5,6-dihydro-4H-pyran, was metered at a uniform rateover 3 hours into the resulting solution. Beginning at the same time asfeed stream 1, feed stream 2, consisting of 22.6 g of tert-butylper-2-ethylhexanoate and 94 g of toluene, was metered in at a uniformrate over the course of 4 hours. Subsequently, the reaction mixture waspost-polymerized at 110° C. for 2 hours more. After the end ofpolymerization, a brown suspension of low viscosity was obtained. At aninternal temperature of 100° C., 318 g of deionized water and 38 g of50% sodium hydroxide solution were added to the reaction mixture, andthe solvent, toluene, was distilled off azeotropically by passing insteam. The solution was cooled and neutralized with 117.0 g of 50%sodium hydroxide solution. This gave a dark brown, slightly cloudysolution with a pH of 7.1 and a solids content of 34.3%. The K value ofa 1% strength aqueous solution of the copolymer (pH 7) was 14.1.

Example 9

A stirred 2 l glass reactor fitted with anchor stirrer, 2 automatic feedmetering devices, reflux condenser and oil-bath heating was charged with147.3 g of maleic anhydride and 1179 g of toluene, and these componentswere heated to reflux under inert gas. Feed stream 1, consisting of amixture of 137.1 g of 6-methoxy-5,6-dihydro-4H-pyran, and 33.7 g of1-octene was metered at a uniform rate over 3 hours into the resultingsolution. Beginning at the same time as feed stream 1, feed stream 2,consisting of 22.6 g of tert-butyl per-2-ethylhexanoate and 94 g oftoluene, was metered in at a uniform rate over the course of 4 hours.Subsequently, the reaction mixture was post-polymerized at 110° C. for 2hours more. After the end of polymerization, a yellow suspension of lowviscosity was obtained. At an internal temperature of 100° C., 318 g ofdeionized water were added to the reaction mixture, and the solvent,toluene, was distilled off azeotropically by passing in steam. Thesolution was cooled and neutralized with 155.0 g of 50% sodium hydroxidesolution. This gave a red-brown, clear solution with a pH of 7.1 and asolids content of 39.1%. The K value of a 1% strength aqueous solutionof the copolymer (pH 7) was 13.8.

Example 10

A stirred 4 l glass reactor fitted with anchor stirrer, 3 automatic feedmetering devices, reflux condenser and oil-bath heating was charged with152.5 g of maleic anhydride and 1179 g of toluene, and these componentswere heated to reflux under inert gas. Feed stream 1, consisting of129.0 g of 6-methoxy-5,6-dihydro-4H-pyran, was metered at a uniform rateover 3 hours into the resulting solution. Beginning at the same at feedstream 1, feed stream 2 consisting of 36.5 g of methacrylic acid wasmetered in at a uniform rate over the course of 3 hours. Likewisebeginning at the same time as feed stream 1, feed stream 3, consistingof 22.6 g of tert-butyl per-2-ethylhexanoate and 94 g of toluene, wasmetered in at a uniform rate over the course of 4 hours. Subsequently,the reaction mixture was post-polymerized at 110° C. for 2 hours more.After the end of polymerization, a yellow suspension of low viscositywas obtained. At an internal temperature of 100° C., 318 g of deionizedwater were added to the reaction mixture, and the solvent, toluene, wasdistilled off azeotropically by passing in steam. The solution wascooled and neutralized with 182.0 g of 50% sodium hydroxide solution.This gave a red-brown, clear solution with a pH of 7.1 and a solidscontent of 40.3%. The K value of a 1% strength aqueous solution of thecopolymer (pH 7) was 20.2.

Example 11

A stirred 4 l glass reactor fitted with anchor stirrer, 2 automatic feedmetering devices, reflux condenser and oil-bath heating was charged with147.0 g of maleic anhydride and 1178 g of toluene, and these componentswere heated to 95° C. under inert gas. Feed stream 1, consisting of171.0 g of 6-methoxy-5,6-dihydro-4H-pyran, was metered at a uniform rateover 5 hours into the resulting solution. Beginning at the same time asfeed stream 1, feed stream 2, consisting of 22.6 g of tert-butylper-2-ethylhexanoate and 94 g of toluene, was metered in at a uniformrate over the course of 6 hours. Subsequently, the reaction mixture waspost-polymerized at 95° C. for 2 hours more. After the end ofpolymerization, a yellow suspension of low viscosity was obtained. At aninternal temperature of 85° C., 318 g of deionized water were added tothe reaction mixture, and the solvent, toluene, was distilled offazeotropically by passing in steam. The solution was cooled andneutralized with 155.0 g of 50% sodium hydroxide solution. This gave ared-brown, clear solution with a pH of 7.1 and a solids content of34.3%. The K value of a 1% strength aqueous solution of the copolymer(pH 7) was 14.5.

Example 12

A stirred 4 l glass reactor fitted with anchor stirrer, 2 automatic feedmetering devices, reflux condenser and oil-bath heating was charged with139.9 g of maleic anhydride and 1179 g of toluene, and these componentswere heated to reflux under inert gas. Feed stream 1, consisting of amixture of 130.2 g of 6-methoxy-5,6-dihydro-4H-pyran and 48.0 of1-dodecene was metered at a uniform rate over 3 hours into the resultingsolution. Beginning at the same time as feed stream 1, feed stream 2,consisting of 22.6 g of tert-butyl per-2-ethylhexanoate and 94 g oftoluene, was metered in at a uniform rate over the course of 4 hours.Subsequently, the reaction mixture was post-polymerized at 110° C. for 2hours more. After the end of polymerization, a two-phase mixtureconsisting of an upper, clear, yellow phase and a lower, brown phase wasobtained. At an internal temperature of 90° C., 318 g of deionized waterwere added to the reaction mixture, and the solvent, toluene, wasdistilled off azeotropically by passing in steam. The solution wascooled and neutralized with 148.0 g of 50% sodium hydroxide solution.This gave a red-brown, clear solution with a pH of 7.1 and a solidscontent of 33.1%. The K value of a 1% strength aqueous solution of thecopolymer (pH 7) was 14.4.

Example 13

A stirred 4 l glass reactor fitted with anchor stirrer, 3 automatic feedmetering devices, reflux condenser and oil-bath heating was charged with27.2 g of maleic anhydride and 1179 g of cyclohexane, and thesecomponents were heated to 70° C. under inert gas. Feed stream 1,consisting of 240.8 g of 6-methoxy-5,6-dihydro-4H-pyran, and feed stream2, consisting of 48.0 g of 1-dodecene, were metered at a uniform rateover 3 hours into the resulting mixture. Beginning at the same time asfeed streams 1 and 2, feed stream 3, consisting of 3.2 g of tert-amylperpivalate and 94 g of cyclohexane, was metered in at a uniform rateover the course of 4 hours. Subsequently, the reaction mixture waspost-polymerized at 70° C. for 2 hours more. After the end ofpolymerization, the solvent was removed by distillation and then 318 gof deionized water were added to the reaction mixture and this mixturewas heated to 100° C. The solution was cooled and adjusted to a pH of 7using sodium hydroxide solution. This gave a brownish solution with asolids content of 42.1%. The K value of a 1% strength aqueous solutionof the copolymer (pH 7) was 36.

Example 14

A stirred 4 l glass reactor fitted with anchor stirrer, 2 automatic feedmetering devices, reflux condenser and oil-bath heating was charged with25.2 g of maleic anhydride and 341 g of tetrahydrofuran, and thesecomponents were heated to reflux under inert gas. Feed stream 1,consisting of 294.7 g of 2,5-dimethoxy-2,5-dihydrofuran, was metered ata uniform rate over 3 hours into the resulting solution. Beginning atthe same time as feed stream 1, feed stream 2, consisting of 6.4 g of2,2'-azobis(2,4-dimethylvaleronitrile) and 50 g of tetrahydrofuran, wasmetered in at a uniform rate over the course of 4 hours. Subsequently,the reaction mixture was post-polymerized at 67° C. for 2 hours more.After the end of polymerization, the solvent was removed by distillationand then 318 g of deionized water were added to the reaction mixture andthis mixture was heated to 100° C. and adjusted to a pH of 7 usingsodium hydroxide solution. This gave a yellow-brown solution with asolids content of 43.1%. The K value of a 1% strength aqueous solutionof the copolymer (pH 7) was 18.3.

Example 15

A stirred 4 l glass reactor fitted with anchor stirrer, 2 automatic feedmetering devices, reflux condenser and oil-bath heating was charged with138.0 g of maleic anhydride and 1179 g of toluene, and these componentswere heated to reflux under inert gas. Feed stream 1, consisting of182.0 g of 2,5-dimethoxy-2,5-dihydrofuran, was metered at a uniform rateover 3 hours into the resulting solution. Beginning at the same time asfeed stream 1, feed stream 2, consisting of 12.8 g of tert-butylper-2-ethylhexanoate and 95 g of toluene, was metered in at a uniformrate over the course of 4 hours. Subsequently, the reaction mixture waspost-polymerized at 110° C. for 2 hours more. After the end ofpolymerization, the internal temperature was reduced to 90° C. and then320 g of deionized water were added to the reaction mixture. Then thesolvent, toluene was distilled off azeotropically by passing in steam,and the solution was cooled and adjusted to a pH of 7 with sodiumhydroxide solution. This gave a red-brown solution with a solids contentof 40.8%. The K value of a 1% strength aqueous solution of the copolymer(pH 7) was 25.5.

Example 16

A stirred 4 l glass reactor fitted with anchor stirrer, 2 automatic feedmetering devices, reflux condenser and oil-bath heating was charged with144.9 g of maleic anhydride and 231 g of butanediol monomethyl ether,and these components were heated to 90° C. under inert gas. Feed stream1, consisting of a mixture of 113.6 g of 6-methoxy-5,6-dihydro-4H-pyranand 61.5 g of styrene, was metered at a uniform rate over 3 hours intothe resulting mixture. Beginning at the same time as feed stream 1, feedstream 2, consisting of 9.6 g of tert-butyl per-2-ethylhexanoate, wasmetered in at a uniform rate over the course of 4 hours. Subsequently,the reaction mixture was post-polymerized at 90° C. for 2 hours more.After the end of polymerization, the internal temperature was raised to160° C. over 45 minutes and the water formed was removed bydistillation. Deionized water and sodium hydroxide solution were added.This gave a neutral, aqueous solution with a solids content of 36.1%.The K value of a 1% strength aqueous solution of the copolymer (pH 7)was 29.2.

Example 17

A stirred 4 l glass reactor fitted with anchor stirrer, 3 automatic feedmetering devices, reflux condenser and oil-bath heating was charged with134.1 g of 6-methoxy-5,6-dihydro-4H-pyran, 650 g of deionized water and3.2 g of sodium dihydrogen phosphate, and these components were heatedto an internal temperature of 80° C. under inert gas. Feed stream 1,consisting of 141.2 g of sodium acrylate, and feed stream 2, consistingof 90 g of a 50% strength aqueous solution of acrylamide, were meteredat a uniform rate over 3 hours into the resulting solution. Beginning atthe same time as feed streams 1 and 2, feed stream 3, consisting of asolution of 3.2 g of 2,2'-azobis-2-methyl propionamidine dihydrochloridein 50 g of deionized water was metered in at a uniform rate over thecourse of 2 hours. Subsequently, the reaction mixture waspost-polymerized at 80° C. for 2 hours more. After the end ofpolymerization, the internal temperature was reduced and the reactionmixture was adjusted to a pH of 7 with dilute sodium hydroxide solution.This gave a clear solution with a solids content of 25.8%. The K valueof a 1% strength aqueous solution of the copolymer (pH 7) was 70.8.

Example 18

A stirred 4 l glass reactor fitted with anchor stirrer, 3 automatic feedmetering devices, reflux condenser and oil-bath heating was charged with133.8 g of maleic anhydride and 1179 g of toluene, and these componentswere heated to reflux under inert gas. Feed stream 1, consisting of 93.4g of 6-methoxy-5,6-dihydro-4H-pyran, and feed stream 2, consisting of92.8 g of dimethylaminopropylmethacrylamide, were metered at a uniformrate over 3 hours into the resulting solution. Beginning at the sametime as feed stream 1, feed stream 3, consisting of 22.6 g of tert-butylper-2-ethylhexanoate and 95 g of toluene, was metered in at a uniformrate over the course of 4 hours. Subsequently, the reaction mixture waspost-polymerized at 110° C. for 2 hours more. After the end ofpolymerization the internal temperature was reduced to 90° C. and then320 g of deionized water were added to the reaction mixture. Then thesolvent, toluene was distilled off azeotropically by passing in steam,and the solution was cooled and adjusted to a pH of 7.1 with sodiumhydroxide solution. This gave a red-brown solution with a solids contentof 40.8%. The K value of a 1% strength aqueous solution of the copolymer(pH 7) was 31.5.

Example 19

A stirred 4 l glass reactor fitted with anchor stirrer, 2 automatic feedmetering devices, reflux condenser and oil-bath heating was charged with147.0 g of maleic anhydride and 1178 g of toluene, and these componentswere heated to 111° C. under inert gas. Feed stream 1, consisting of171.0 g of 6-methoxy-5,6-dihydro-4H-pyran, was metered at a uniform rateover 2 hours into the resulting solution. Beginning at the same time asfeed stream 1, feed stream 2, consisting of 22.6 g of tert-butylper-2-ethylhexanoate and 95 g of toluene, was metered in at a uniformrate over the course of 4 hours. Subsequently, the reaction mixture waspost-polymerized at 110° C. for 2 hours more. 209.0 g of tridecylaminewere added to the resulting pale brown suspension of low viscosity, andthe reaction mixture was heated at 160° C. for 45 minutes; subsequently,200 g of deionized water were added to the reaction mixture and theorganic solvent was distilled off azeotropically by passing in steam. Atthe end of steam distillation a brown dispersion was present, which wascooled and adjusted to a pH of 7 with dilute sodium hydroxide solution.This gave a brown dispersion with a solids content of 26.3%. The K valueof a 1% strength aqueous solution of the copolymer (pH 7) was 19.9.

Example 20

A stirred 4 l glass reactor fitted with anchor stirrer, 2 automatic feedmetering devices, reflux condenser and oil-bath heating was charged with147.0 g of maleic anhydride, 400 g of toluene and 3.2 g of a maleicanhydride and diisobutene copolymer, 60% of whose anhydride groups havebeen esterified with n-decanol and these components were heated to 111°C. under inert gas. Feed stream 1, consisting of 171.0 g of6-methoxy-5,6-dihydro-4H-pyran, was metered at a uniform rate over 3hours into the resulting solution. Beginning at the same time as feedstream 1, feed stream 2, consisting of 22.6 g of tert-butylper-2-ethylhexanoate and 80 g of toluene, was metered in at a uniformrate over the course of 4 hours. Subsequently, the reaction mixture waspost-polymerized at 110° C. for 2 hours more. After the end ofpolymerization, a pale brown suspension of low viscosity was obtained.200 g of deionized water was added to the reaction mixture, and theorganic solvent was distilled off azeotropically by passing in steam. Atthe end of steam distillation a brown solution was present, which wascooled and neutralized with 158.0 g of 50% sodium hydroxide solution.This gave a dark brown, clear solution with a pH of 7.3 and a solidscontent of 34.4%. The K value of a 1% strength aqueous solution of thecopolymer (pH 7) was 16.2.

Example 21

A stirred 4 l glass reactor fitted with anchor stirrer, 2 automatic feedmetering devices, reflux condenser and oil-bath heating was charged with147.0 g of maleic anhydride, 400 g of toluene and 3.2 g of polyoctadecylvinyl ether and these components were heated to 110° C. under inert gas.Feed stream 1, consisting of 171.0 g of 6-methoxy-5,6-dihydro-4H-pyran,was metered at a uniform rate over 3 hours into the resulting solution.Beginning at the same time as feed stream 1, feed stream 2, consistingof 22.6 g of tert-butyl per-2-ethylhexanoate and 80 g of toluene, wasmetered in at a uniform rate over the course of 4 hours. Subsequently,the reaction mixture was post-polymerized at 110° C. for 2 hours more.After the end of polymerization, a pale brown suspension of lowviscosity was obtained. 200 g of deionized water was added to thereaction mixture, and the organic solvent was distilled offazeotropically by passing in steam. At the end of steam distillation aslightly cloudy brown solution was present, which was cooled andneutralized with 158.0 g of 50% sodium hydroxide solution. This gave adark brown, clear solution with a pH of 7.1 and a solids content of32.7%. The K value of a 1% strength aqueous solution of the copolymer(pH 7) was 13.9.

Example 22

A stirred 4 l glass reactor fitted with anchor stirrer, 2 automatic feedmetering devices, reflux condenser and oil-bath heating was charged with147.0 g of maleic anhydride, 400 g of toluene and 3.2 g of a maleicanhydride and styrene copolymer having a number-average molecular weightof 110,000 and these components were heated to 111° C. under inert gas.Feed stream 1, consisting of 171.0 g of 6-methoxy-5,6-dihydro-4H-pyranand 16.0 g of n-dodecylmercaptan, was metered at a uniform rate over 3hours into the resulting solution. Beginning at the same time as feedstream 1, feed stream 2, consisting of 22.6 g of tert-butylper-2-ethylhexanoate and 80 g of toluene, was metered in at a uniformrate over the course of 4 hours. Subsequently, the reaction mixture waspost-polymerized at 110° C. for 2 hours more. After the end ofpolymerization, a pale brown suspension of low viscosity was obtained.200 g of deionized water was added to the reaction mixture, and theorganic solvent was distilled off azeotropically by passing in steam. Atthe end of steam distillation a brown solution was present, which wascooled and neutralized with 155.0 g of 50% sodium hydroxide solution.This gave a dark brown, clear solution with a pH of 7.1 and a solidscontent of 36.6%. The K value of a 1% strength aqueous solution of thecopolymer (pH 7) was 11.2.

Application in Leather Production

Example 23

Self-Tanning

Pickled cattle pelt having a split thickness of 3 mm was treated with4%, based on solids content, of a copolymer prepared as in Example 2,the pelt being in 50% water and 50% pickling liquor at 20° C. and at apH of 3.0. The milling time was 180 minutes. The liquor was then heatedto 40° C., 0.8 % of commercially available magnesium oxide was added,and the mixture was milled at this temperature for 180 minutes. It wasthen cooled to room temperature and agitated overnight in the millingdrum. The pH was subsequently 4.0, and the mixture was heated to 40° C.and adjusted to a pH of 6.8 by portionwise addition of sodiumbicarbonate over 5 hours. The leather was rinsed with water and rackedovernight. The shrinkage temperature was 81° C., as against 68° C. forthe untreated pelt.

Example 24

Retanning of Chrome-Tanned Leather to Give Upholstery Leather

A cattle wet blue with a shaved thickness of 1.2 mm was first of allwashed with 300% of water at 30° C. and was then deacidified in 100%liquor at 30° C. with sodium formate and sodium bicarbonate to a pH ofabout 5.0. After brief rinse, the leather was drum-retanned at 40° C. in100% liquor using 3%, based on the solid product, of the polymerprepared in Example 1. After milling for 90 minutes, the leather wasrinsed again and dyed in 100% liquor at 50° C. using 1% of acommercially available metal complex leather dye, fatliquored with 8% ofa commercially available fatliquor, and adjusted to a pH of 4.0 usingformic acid. The leather was racked overnight, then wet-stretched anddried. Sawdusting, staking and drumming gave a soft leather with verygood body, intense, level coloration and good through-coloring insection. The mill grain showed a fine, uniform appearance, even at theflanks and sides.

Examples 25 and 26

Working in a manner similar to that of Example 24, 3%, based on thesolids content of the products, of each of the copolymers from Examples3 and 4 were used for retanning chrome cattle leather to give upholsteryleather. In both cases, a very full-bodied and soft leather was obtainedwhich was notable in particular for a good intense color with goodthrough-coloration and a uniform mill grain.

Comparative Example A

Retanning of Chrome-Tanned Leather to Give Upholstery Leather

A commercially available polymer based on methacrylic acid was used bythe method similar to that of Example 24 to retan chrome cattle leatherto give upholstery leather. The resultant leather was lower in body andhad a paler color for the same amount of dye, both on the surface and insection.

Example 27

Retanning of Chrome-Tanned Leather to Give Shoe Uppers Leather at HighPolymer Concentration

A cattle wet blue with a shaved thickness of 1.5 mm was, in aconventional manner, rinsed, washed and subsequently deacidified to a pHof 4.5 in 100% liquor using sodium formate at 30° C. After washing, theleather was milled for 90 minutes at 40° C. in 100% liquor containing5%, based on the solids content, of the copolymer from Example 1. Theleather was then washed again and dyed in 100% liquor at 50° C. for 20minutes using 1% of a commercially available leather dye. Fat liquoringtook place in the same liquor using 4% of a commercially available fatliquor. The pH was then adjusted to 3.6 using formic acid. After a briefrinse, the leather was stretched, dried, treated with sawdust andstaked, giving a leather of good body and with a firm grain, having arounded, supple handle and a very level and intense coloration.

Examples 28 to 48

Retanning of Chrome-Tanned Leather to Give Shoe Uppers Leather at HighPolymer Concentration

Working in the same way as in Example 27, 5%, based on solids content,of each of the copolymers from Examples 2 to 22 were used as retanningagent. In every case they gave very full-bodied and intensely coloredleathers whose softness varied depending on the comonomer. In comparisonto the above examples, commercial polymers based on acrylic acid, whenprocessed in the same way, led to severely hardened, rough leathers withan unpleasant handle.

Example 49

Retanning of Chrome-Tanned Leather to Give Shoe Uppers Leather at LowConcentration of Polymer Tanning Agent

A cattle wet blue with a shaved thickness of 1.8 mm was, in theconventional manner, rinsed, washed and then deacidified to a pH of 4.4in 100% liquor using sodium formate. After rewashing, it was then firstof all milled for 30 minutes in 100% liquor at 30° C. using 1.0% of acommercially available dispersant (phenolsulfonic acid-formaldehydecondensation product). It was then retanned in the same liquor at 30° C.using 1%, based on solids content, of the copolymer from Example 1.After milling for 90 minutes, the leather was rinsed again. Dyeing wascarried out in 200% liquor at 40° C. using 1% of a commerciallyavailable leather dye, and fat liquoring was carried out using 4% of acommercially available fat liquor. The pH was then adjusted to 3.6 withformic acid. After a brief rinse the leather was stretched, dried,treated with sawdust and staked. The resultant leather was of good bodyand softness, had a very good firm grain and showed very good dyeingbehavior, in terms of both surface dyeing and penetration of the dyeinto the cross-section of the leather.

Comparative Example B

Example 24 was repeated using, instead of the product from Example 8, acommercially available tanning agent based on acrylic acid. In this casethe body, softness and dyed appearance of the leather were much poorerthan in Example 24.

We claim:
 1. A method of self-tanning, pre-tanning or assist tanningleather pelts or skin pelts or of retanning leather or skins, whichcomprises using, as a tanning agent, an aqueous solution or dispersionof copolymers composed ofA) from 5 to 95 mol % of ethylenicallyunsaturated mono- or dicarboxylic acids having 3 to 10 carbons, theiranhydrides, their alkali metal, alkaline earth metal or ammonium salts,or mixtures thereof, B) from 5 to 95 mol % of ethylenically unsaturatedacetals, ketals or orthocarboxylic esters of the formula I ##STR8##wherein R¹ and R² independently are hydrogen, C₁ -C₁₀ -alkyl, C₁ -C₁₀-alkoxy, amino, C₁ -C₄ -alkylamino or di-C₁ -C₄ -alkylamino,R³, R⁴, R⁵,R⁶, R⁸, R⁹, R¹⁰ and R¹¹ independently are hydrogen C₁ -C₁₀ -alkoxy,amino, C₁ -C₄ -alkylamino, di-C₁ -C₄ -alkylamino, C₆ -C₁₄ -aryl, C₇ -C₁₈-aralkyl, carboxyl, C₁ -C₂₀ -alkoxycarbonyl, C₂ -C₁₈ -alkyl interruptedby 1-5 nonadjacent oxygens, or are sulfo or phosphono, R⁷ is hydrogen,C₁ -C₁₀ -alkyl, C₆ -C₁₄ -aryl, C₇ -C₁₈ -aralkyl or C₁ -C₁₀ -acyl, R¹² ishydrogen, C₁ -C₁₀ -alkyl, C₁ -C₁₀ -alkoxy, hydroxyl or C₁ -C₁₀ -acyloxy,and a, b, c and independently are 0 or 1, it also being possible for R²and R⁴ together to form a 1,3- or 1,4-alkylene group of 3 to 12 carbonsand for R⁵ and R⁷ together to form a 1,2- or 1,3-alkylene group of 2 to12 carbons, and C) from 0 to 70 mol % of other copolymerizablemonomers,or their hydrolysis products or polymer-analogous reactionproducts.
 2. A method as claimed in claim 1, wherein the monomers Aincluded in the copolymers are acrylic acid, methacrylic acid, maleicacid, itaconic acid or maleic anhydride.
 3. A method as claimed in claim1, wherein the monomers B included in the copolymers are5,6-dihydro-4H-pyrans of the formula Ia ##STR9## or 2,5-dihydrofurans ofthe formula Ib ##STR10## wherein R¹, R², R⁴, R⁵, R⁷, R⁸, R⁹ and R¹² areas defined above.
 4. A method as claimed in claim 1, wherein themonomers B included in the copolymers are 6-methoxy-5,6-dihydro-4H-pyranor 2,5-dimethoxy-2,5-dihydrofuran.
 5. A method as claimed in claim 1,wherein the monomers C included in the copolymers are methyl(meth)acrylate, ethyl (meth)acrylate, lauryl (meth)acrylate, butene,isobutene, 2,4,4-trimethyl-1-pentene, 1-octene, C₈ -C₁₀ olefin,1-dodecene, C₁₂ -C₁₄ olefin, C₂₀ -C₂₄ olefin, oligopropene, oligohexene,oligooctadecene, reactive polyisobutene, vinyl stearate,2-acrylamido-2-methylpropanesulfonic acid, ethylhexyl vinyl ether,styrene, acrolein or acrylonitrile.